1. Field of the Invention
The present invention relates to apparatus for measuring and displaying the tempo corresponding to the setting of a manually adjustable tempo control, and for controlling the tempo rate in an electronic musical instrument in response to the setting of the manual control by the musician, and more specifically to a tempo control that is self-calibrating and which has a non-linear relationship between the mechanical position of the manual control and the tempo selected.
2. Description of the Prior Art
Metronomes providing audible beats corresponding to a particular time signature or tempo rate are well-known in the art. As noted in the co-pending U.S. patent application Ser. No. 143,269 entitled "Rhythm Rate and Tempo Monitor for Electronic Musical Instruments Having Automatic Rhythm Accompaniment," filed Apr. 24, 1980, and which is the parent of continuation application Ser. No. 345,798, filed Feb. 4, 1982, titled "Rhythm Rate and Tempo Monitor for Electronic Musical Instruments having Automatic Rhythm Accompaniment" and assigned to the same assignee as the instant application and assigned to the Baldwin Piano & Organ Company, such prior art devices have ranged from simple mechanical devices to more elaborate electronic systems. It is also noted that some prior art metronome devices included visible indicators for augmenting the audible beats. The foregoing patent application describes a microprocessor based system for monitoring tempo rate in an electronic musical instrument of the type having means for automatically producing a preselected rhythm accompaniment having a desired tempo, such as that described and illustrated in U.S. Pat. No. Re. 29,144.
In a first mode of operation the system described in the foregoing patent application permits the musician to adjust the rhythm rate of a rhythm accompaniment unit visually by a digital display of quarter notes per minute in the absence of an audible rhythm output. In a second mode of operation the foregoing system can be used with the rhythm unit on as a timing indicator for player synchronization with rhythm. In this second mode of operation, the timing indicator appears on a display consisting of four adjacent numeric character indicators. The down-beat indication is displayed as a numeric 1 in the left-most display device, the second beat is displayed in the adjacent display device as numeric 2, etc., so that the effect of motion is imparted to the display. Processing circuitry automatically interprets the time signature of the rhythm accompaniment produced by the rhythm accompaniment unit to provide the proper number of beats displayed as numeric characters per display sequence.
In the foregoing patent application the rhythm rate and tempo monitor system is implemented by a microprocessor. The tempo rate is determined by the setting of a rate potentiometer which determines the charging time of an associated capacitor. Initially, the microprocessor, by executing appropriate instructions stored in an internal ROM, discharges the capacitor and begins a counting loop. The count accumulated during the charging time provides a measure of the resistive setting of the rate potentiometer, and consequently the tempo rate of the rhythm accompaniment unit. When the rhythm unit is off, the count obtained from the rhythm potentiometer setting is converted to a tempo rate number by means of a look-up table contained within the microprocessor ROM. This number is then displayed on the numeric character display as the appropriate number of quarter notes per minute. When the rhythm unit is on, a clock pulse, related to the rhythm potentiometer setting, is gated to the rhythm unit. The clock pulse operates an address counter which is used to generate the rhythm pattern. Using the address outputs from the address counter, the microprocessor sequentially displays the appropriate numeric character in the proper display device. In one embodiment, the displays are blanked between successive character displays to provide a scanned timing indicator.
The present invention, on the other hand, provides improved means for accomplishing the features of the foregoing system. Specifically, the prior art rhythm rate and tempo monitor system does not include means for compensating for inaccuracies or drift in the values of the capacitor and rate potentiometer. Another feature of the prior art system is that to allow for drift in the resistance of the potentiometer, considerable dead space must be provided near the maximum setting of the potentiometer to ensure that a reading corresponding to the maximum tempo rate is always obtained. This dead space is undesirable because the musician operating the instrument expects to obtain a maximum reading near the maximum position of the potentiometer. In addition, the present invention provides means for introducing a non-linear relationship between capacitor charging time and the time interval between rhythm beats. This is done so that the steps in the rate displayed are finer in the middle of the range of potentiometer settings than near the two extreme potentiometer settings. Thus, settings in the range most frequently selected by the musician can be selected with the greatest accuracy.